As illustrated in FIG. 1 of the attached drawings, a cascade-type thrust reverser 3 such as this, of the type known as the natural type, generally comprises a cowling 1 in which there is formed an opening equipped with cascades 6 (of vanes) which, when the gases are in the direct-thrust situation, is closed by a sliding cowl 7 (see the upper half of FIG. 1) and which, in the thrust-reversal situation, is uncovered by a downstream (with reference to the direction in which the gases flow) translational movement of the sliding cowl 7 (see the lower half of FIG. 1).
A fan duct 5 is defined between an inner skin 2 (a cowl surrounding the engine) and an outer skin into which the inner skin of the sliding cowl 7 fits in the direct-thrust situation.
The inner skin of the sliding cowl 7 comprises an annular part extending radially inward and capable, in a thrust-reversal situation, of butting against a larger-diameter annular part (which forms a hump) of the inner skin 2 of the fan duct in order more or less, and in a “natural” way, to block the cold stream passing through the fan duct 5 with a view to deflecting it forward through the opening that has the vanes 6.
For more details regarding this type of reverser, reference may be made to patent documents FR 2 132 380, FR 1 349 738 and U.S. Pat. No. 4,232,516.
The annular “hump” of the cowl 2 surrounding the engine means that the nacelle has to have aerodynamic lines that encompass large diameters, whereas aircraft manufacturers would prefer increasingly short landing gear which entails reducing the diameter of nacelles carried under the wing.
Furthermore, the aerodynamic lines of the nacelle may sometimes fail to leave the annular hump of the cowl 2 a space close enough to the upstream part of the fixed structure 4 of the reverser (bearing in mind the fact that the maximum retraction travel of the sliding cowl 7 is relatively limited). What this means is that the sliding cowl 7 has to retract a long way, often beyond the length of the cascade vanes 6 which length is itself limited by the fine lines of the sliding cowl 7 in the direct-thrust situation.
Finally, the aerodynamic lines at the downstream part of the siding cowl 7 are often very tapered in order not to encroach too far into the radial volume of the nacelle, and “sandwich” structures to provide optimal sound-deadening cannot be included.